Retinal acuity testing device

Abstract

Optical measuring and testing apparatus incorporating a holographically recorded, single-frequency, optically thin phase grating. When this phase grating is illuminated by a quasi-monochromatic spatially coherent light source, it acts as a basic common path interferometer and constitutes a highly efficient source for a high contrast, stable, interference fringe pattern. In one embodiment, elements are repositioned to move the light source with respect to the grating thereby to alter the number of fringes in a given area. In another embodiment, elements are rotated about the optical axis of the apparatus to control the orientation of the fringe pattern. Provision is also made for allowing the examiner to view the patient's eye pupil during testing.

What I claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. Opthalmic apparatus for producing an interference pattern on the retina of an eye, said apparatus comprising; A. interference pattern generating means for generating a first diffraction and a second diffraction that are of different order, that have equal strength and that overlap thereby to produce a high-contrast, low-noise interference pattern in the area of overlap, and   B. focusing means positioned to receive the interference pattern from said interference pattern generating means for projecting the interference pattern onto the retina from only two point sources of light in the eye pupil.   
     
     
       2. An apparatus as recited in claim 1 wherein said interference pattern generating means includes: i. quasi monochromatic, spatially coherent light source means, and   ii. holographically recorded, single frequency phase grating means responsive to the energy from said light source means for producing the diffractions.   
     
     
       3. Apparatus as recited in claim 2 additionally comprising: C. second focusing means between said light source means and said grating means for focusing the light at a focal point that is displaced toward said light source means from said grating means, and   D. positioning means connected to said second focusing means and said grating means for moving the focal point with respect to the grating means thereby to vary the interference pattern.   
     
     
       4. Apparatus as recited in claim 3 wherein said second focusing means includes: i. negative lens means for receiving light from said light source means,   ii. objective lens means for focusing light from said negative lens means at the focal point, and   iii. filter means connected between said light source means and said negative lens means for varying the intensity of the light from said light source means.   
     
     
       5. Apparatus as recited in claim 1 wherein said focusing means comprises: i. eye piece means, and   ii. aperture means positioned between said grating means and said eye piece means.   
     
     
       6. Apparatus as recited in claim 5 additionally comprising optical viewing means interposed between said eye piece means and said grating means for enabling the viewing of the eye through said eye piece means. 
     
     
       7. Apparatus as recited in claim 6 wherein the interference pattern from said grating means is projected along an axis, said optical viewing means comprising: i. beamsplitting means disposed on the axis between said grating means and said eye piece means,   ii. second light source means for projecting light orthogonally to the axis to said beamsplitting means, said beamsplitting means thereby directing the light through said eye piece means to the eye, and   iii. viewing means for receiving reflected light from said eye piece means through said beamsplitting means for viewing the eye.   
     
     
       8. Apparatus as recited in claim 7 wherein said viewing means comprises cross polarizing means on said axis. 
     
     
       9. Apparatus as recited in claim 7 wherein said optical viewing means includes: i. second beamsplitting means disposed on said axis between said first beamsplitting means and said grating means,   ii. eye piece means aligned on a viewing axis intercepting said second beamsplitting means and said first axis,   iii. first and second cross polarizing means disposed on the viewing axis between said eyepiece and said second beamsplitting means and on said first axis between said grating means and said second beamsplitting means,   iv. lens means disposed between said first cross polarizing means and said second beamsplitting means for producing a viewable image, and   v. mirror means disposed on an extension of the viewing axis on a side of said second beamsplitting means opposite to said lens means.   
     
     
       10. Apparatus as recited in claim 5 wherein said focusing means additionally comprises: 
     
     
       i. dove prism means disposed on the axis between said grating means and said eye piece means, and ii. means for rotating said dove prism thereby to rotate the interference pattern produced on the retina.